net/netip: check if address is v6 mapped in Is methods

net/netip: check if address is v6 mapped in Is methods

In all of the Is* methods, check if the address is a v6 mapped v4
address, and unmap it if so.

Thanks to Enze Wang of Alioth (@zer0yu) and Jianjun Chen of Zhongguancun
Lab (@chenjj) for reporting this issue.

Fixes #67680
Fixes CVE-2024-24790

Change-Id: I6bd03ca1a5d93a0b59027d861c84060967b265b0
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/1460
Reviewed-by: Russ Cox <rsc@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/590316
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>